Method for efficiently recovering platinum group elements from copper-iron scrap

ABSTRACT

A method for efficiently recovering a platinum group element comprises melting copper-iron scrap containing a platinum group element, forming the melt into two liquid phases, a molten copper phase containing at least one rare metal selected from the group consisting of Nd, Pr, and Dy and a molten iron phase having a carbon concentration of at least 1 mass %, with the carbon contained in the molten iron phase being derived from carbon contained in the melt, separating the two liquid phases, recovering the molten copper phase, and separating and recovering from the molten copper phase a platinum group element dissolved therein. The copper-iron scrap may contain a rare metal, or a member containing a rare metal may be added to the melt with a preferred total concentration of rare metals in the melt being at least 1 mass %.

TECHNICAL FIELD

This invention relates to a method in which scrap containing copper andiron (referred to in this description as copper-iron scrap) and furthercontaining a platinum group element typified by platinum (Pt) isseparated into a molten copper phase containing neodymium (Nd),dysprosium (Dy), and/or praseodymium (Pr) (these metals will becollectively referred to below as rare metals) and a molten iron phasecontaining carbon in a predetermined concentration and the platinum isseparated and recovered by concentrating the platinum contained in thecopper-iron scrap in the molten copper phase with a high distributionratio.

BACKGROUND ART

Various types of products including metal products made of iron andsteel, copper, copper alloys and the like such as industrial equipment,transport equipment such as automobiles, household electricalappliances, office automation equipment, and electrical equipment,plastic products, and other types of products are manufactured in largequantities. These products typically comprise electrical parts mountedon a frame or cabinet. Structural members such as frames often useferrous materials, and electrical components often use materialscontaining copper (copper and copper alloys) as wiring. Electricalcomponents use a wide variety of valuable metals in order to exhibitdesired device properties. In recent years, there has been a tendency touse an increasing variety and increasing amounts of these metals inorder to increase the performance of products.

When these products are discarded, since they contain copper and iron,they become copper-iron scrap. There is much prior art concerningrecovery of copper and iron from this copper-iron scrap by separatingcopper and iron into two liquid phases, i.e., a copper phase and an ironphase by a melting process. In a method known to be superior, copper andiron can be efficiently separated and recovered by adding carbon or thelike in the melting process. In addition to such a method, it is alsoknown that the alloying elements and precious metals contained incopper-iron scrap are dissolved in a molten copper phase or a molteniron phase and separated and recovered.

For example, Patent Document 1 discloses a method of recovering metalsfrom copper-iron scrap in which carbon is dissolved in a melt obtainedby melting copper-iron scrap in a furnace to form the melt into twoliquid phases, a molten copper phase and a molten iron phase, andseparating the two phases to recover copper and iron separately, whereinthe furnace used for melting the copper-iron scrap is a melting furnacehaving a packed bed of a carbonaceous material, and a carbonaceousmaterial with an average particle diameter of 20-70 mm is used to formthe packed bed of the melting furnace. It also discloses that valuablemetals are separated in an individual phase and recovered. However,there is a desire for a method capable of efficiently recoveringspecific types of metals.

Typical examples of metals for which an efficient recovery method isdesired are platinum group elements. Among platinum group elements,platinum (Pt) which is the most industrially useful is employed as acatalyst for automotive exhaust gas processing, for example. However,there is a limited number of countries which produce platinum.Therefore, platinum is a typical precious metal which it is desired torecover from existing used products.

As a method of recovering platinum from copper-iron scrap containingplatinum, Non-Patent Document 1 discloses a method in which carbon isdissolved in an iron phase and a molten copper phase and a molten ironphase are separated in an iron (Fe)-copper (Cu)-carbon (C) system. Dueto the difference in specific gravity, the molten copper phase and themolten iron phase are separated as a lower phase and an upper phase,respectively, and recovered separately. The distribution of platinum inthese two phases is determined by the interaction between platinum andiron and between platinum and copper. It is reported that thedistribution ratio of platinum [mass % Pt]_(in cu)/[mass % Pt]_(in Fe-C)(the mass % of platinum in copper/the mass % of platinum incarbon-containing iron) is around 1, so platinum is distributed roughlyequally in the two phases.

Patent Document 2 discloses that in a method of separating two liquidphases of a copper and iron phases in an iron (Fe)-copper (Cu)-carbon(C)-phosphorus (P) system, platinum is concentrated in the iron phase.

In addition to the above-described platinum group elements, a usefulmetal for which an improved recovery method is desired is neodymium(Nd). The production of Nd magnets, which is the principal use ofneodymium, is said to be around 10,000 tons per year. For example, asingle hybrid automobile uses one kg of Nd magnets, and the amount ofcopper-iron members including Nd magnets in the automobile (in themotor, alternator, sensors, and the like: iron:copper=80:20) isapproximately 50 kg. One kilogram of Nd magnets contains a total ofaround 300-400 grams of rare metals such as neodymium (Nd), dysprosium(Dy), and praseodymium (Pr). As Nd magnets are not reused as magnets,there is a desire for an effective processing method after recovery ofproducts.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: JP 2009-185369 A-   Patent Document 2: JP 2004-083962 A

Non-Patent Documents

-   Non-Patent Document 1: Yamaguchi et al, Shigen to Zairyo (Resources    and Materials), Vol. 113 (1997), page 1110

DISCLOSURE OF INVENTION

In the method disclosed in Non-Patent Document 1 which is a copper andiron two liquid phase separation method in an iron (Fe)-copper(Cu)-carbon (C) system, the distribution of platinum is determined bythe interaction between platinum and iron and by the interaction betweenplatinum and copper. Therefore, the distribution ratio [mass %Pt]_(in Cu)/[mass % Pt]_(in Fe-C) is around 1, and plutinum isdistributed nearly equally in the two phases. Namely, Non-PatentDocument 1 suggests that with an iron (Fe)-copper (Cu)-carbon (C)system, it is difficult to select an efficient process in which platinumis concentrated in one of the phases and is recovered from theconcentrated phase.

In contrast, according to the method disclosed in Patent Document 2, itis possible to concentrate platinum in a molten iron phase, i.e., toconcentrate it in one of the phases). However, recovering platinum froma molten iron phase is difficult in actual practice. A method ofdissolving an iron phase in an acid solution and then collectingplatinum by aqueous solution electrolysis is conceivable. In this case,it is necessary to dissolve all of the iron phase in acid in order torecover platinum, which is present in a small amount compared to ironwhich is the medium. Therefore, a large amount of acid is necessary, andthis creates the problem of disposing a large amount of waste acidsolution which is formed. Accordingly, for practical purposes, it isnecessary to develop a new efficient method of separating and recoveringplatinum from an iron phase.

In an existing copper refining process, due to the presence of platinumcontained in a copper concentrate used as a raw material, a recoverymethod for platinum in a copper refining process has already beenestablished. The details of a copper refining process are as follows.First, a copper concentrate is separated into slag, matte, and off-gasin a flash smelting furnace. Iron is removed in the slag phase, andsulphur is removed as off-gas. The matte is then oxidized in a converterand separated into slag, crude copper, and off-gas. The crude copper ispassed through a refining furnace to an electrolytic tank in which it isseparated into electrolytic copper, an anode slime, and an electrolyte.Platinum which was separated from copper is concentrated in the anodeslime, and the platinum is recovered by subjecting the slime toelectrolysis after being dissolved in an acid. Thus, the copper phasecan be processed by placing it into a converter in the current copperrefining process, and subsequently according to the conventional copperrefining process, platinum contained in the copper phase can berecovered.

From the above, for recovery of platinum from copper-iron scrap, ifplatinum can be concentrated in a molten copper phase, it becomespossible to recover the platinum by applying an existing copper refiningprocess to the subsequent processing of the molten copper phase.

The object of the present invention is to provide a means forefficiently recovering platinum group elements from copper-iron scrapcontaining platinum group elements typified by platinum by efficientlyconcentrating platinum group elements in a molten copper phase which isobtained from the copper-iron scrap.

Upon investigation of the distribution of rare metals in a copper phaseand an iron phase and the interaction of platinum group elements andparticularly platinum with these rare metals as well as the effect ofthere elements on separation of copper and iron liquid phases, thepresent inventors found that rare metals are concentrated in a copperphase and that platinum, which has a thermodynamic affinity for raremetals, is attracted by the rare metals into the copper phase andconcentrated in the copper phase with a high distribution ratio.

The present invention, which was completed based on this finding, is asfollows.

(1) A method for recovering platinum in copper-iron scrap characterizedby melting copper-iron scrap containing a platinum group element,allowing the resulting melt to contain a carbon source so as to form themelt into two liquid phases, one being a molten copper phase containingone or more rare metals selected from the group consisting of Nd, Pr,and Dy and the other being a molten iron phase having a carbonconcentration of at least 1 mass %, separating the two liquid phases torecover the molten copper phase, and separating and recovering platinumdissolved in the molten copper phase from the molten copper phase.

(2) A method as set forth above in (1) wherein the molten copper phaseis made to contain the rare metals by using scrap containing the raremetal as the copper-iron scrap.

(3) A method as set forth above in (1) wherein the molten copper phaseis made to contain the rare metals by adding a member containing therare metal to the melt.

(4) A method as set forth above in (1) wherein the total concentrationof the rare metals contained in the molten copper phase is at least 1mass %.

(5) A method as set forth in claim 1 wherein the melt contains at leastone distribution promoting metal selected from the group consisting ofSc, Li, Ca, Mg, Y, La, K, Sr, Th, Ga, Ba, Na, and Rb, and/or at leastone distribution inhibiting metal selected from the group consisting ofTi, Zr, Hf, Nb, V, U, and Ta, and the molten copper phase and the molteniron phase which were obtained by separating the melt into two liquidphases satisfy the following Equation (i).

2.2Sc+1.7Li+1.4Ca+1.2Mg+1.2Y+Nd+Pr+0.87Dy+0.79La+0.78K+0.74Sr+0.61Th+0.52Ga+0.51Ba+0.50Na+0.45Rb+0.36Pu+0.35Cs+0.24Sn+0.23In+0.23Zn−(1.2Ti+1.2Zr+0.51Hf+0.49Nb+0.29V+0.29U+0.25Ta)>1.0mass %  (i)

In Equation (i), the symbol for each element indicates the massconcentration (unit: mass %) of the corresponding element in the moltencopper phase with respect to the mass of the molten copper phase in thecase of the distribution promoting metals and the rare metals, and itindicates the mass concentration (unit: mass %) of the correspondingelement in the molten iron phase with respect to the mass of the molteniron phase in the case of the distribution inhibiting metals.

According to the present invention, it is realized that platinum, whichis considered to be difficult to efficiently recover because of itsdistribution ratio between a copper and an iron liquid phase which isnormally around 1, can be concentrated in a copper phase and easilyrecovered with high efficiency based on conventional technology. Thepresent invention can also concentrate platinum group elements otherthan platinum in the copper phase. Therefore, the present inventionprovides a means for efficiently recovering platinum group elements.Furthermore, rare metals are concentrated in the copper phase during thecourse of concentrating platinum group elements, so Nd and other raremetals can also be efficiently recovered.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a graph showing the effect of element i in a copper phase onthe distribution ratio of platinum (Pt).

FIG. 2 is a graph showing the effect of neodymium (Nd) in a copper phaseon the distribution ratio of platinum (Pt).

MODES FOR CARRYING OUT THE INVENTION

When copper-iron scrap such as household electrical appliances whichcontains platinum group elements and particularly platinum and whichincludes neodymium magnets containing rare metals such as neodymium(Nd), dysprosium (Dy), and praseodymium (Pr) is melted in a carbonaceousmaterial-packed bed or the like so as to dissolve carbon in theresulting melt and the melt is separated into two liquid phases, i.e., acopper phase and an iron phase, the rare metals are concentrated in thecopper phase. As the rare metals are concentrated in the copper phase,the distribution ratio of platinum between the copper phase and the ironphase varies due to the influence of the rare metals.

The present invention is based on this principle, and makes it possibleto obtain a copper phase in which a platinum group element andparticularly platinum is concentrated. As a result, the platinum groupelement can be efficiently separated and recovered from copper-ironscrap. In addition, rare metals are also concentrated in the copperphase, so it is possible to also recover rare metals at the same time.

The present invention will be explained in greater detail.

In the present invention, by causing a melt obtained by meltingcopper-iron scrap to contain a carbon source, the melt is allowed toseparate into two liquid phases in the form of a molten copper phase anda molten iron phase (more precisely, a molten liquid phase having aprincipal component of iron-carbon). As disclosed in Patent Documents 1and 2, if the carbon concentration in a molten iron phase is made atleast 1 mass percent and preferably at least 4 mass percent, the amountof copper contained in the molten iron phase can be reduced.Accordingly, a decrease in the amount of copper recovered as a moltencopper phase is suppressed, which contributes to an increase in therecovery rate of platinum group elements. As described below, increasingthe carbon concentration in the molten iron phase increases thedistribution of a platinum group element and particularly platinum inthe molten copper phase. Therefore, from this standpoint as well, it ispreferable to set the carbon concentration in the molten iron phase to ahigh level.

There is no limitation on a way of supplying a carbon source to themelt. Resins which are incorporated in carbon-iron scrap can be used asa carbon source, or a known carbonaceous material such as coal can beadded to the copper-iron scrap or melt as a carbon source.Alternatively, a graphite crucible can be used as a vessel for meltingthe copper-iron scrap, and carbon can be supplied from the crucible.

In the following explanation, the case will be explained in whichrecovery is carried out of platinum (Pt) as a typical example of aplatinum group element.

The equilibrium reaction between platinum (Pt) in a copper phase andplatinum in an iron phase is expressed by Equation (1).

Pt(inCu)=Pt(inFe—C)  (1)

Since the chemical potentials are equal in an equilibrium state,Equation (2) is established. As shown by Equation (3) which is based onthe relationship in Equation (2), the distribution ratio of platinumbetween the copper phase and the iron phase X_(Pt in Cu)/X_(Pt in Fe-C)is given by the activity coefficients of platinum γ_(Pt in Cu) andγ_(Pt in Fe-C) in the respective phases.

RT·ln a _(Pt in Cu)=RT·ln a _(Pt in Fe-C)  (2)

X_(Pt in Cu)/X_(Pt in Fe-C)=γ_(Pt in Fe-C)/γ_(Pt in Cu)  (3)

where a_(Pt in Cu) and a_(Pt in Fe-C) indicate the activity of platinum(Pt) in the copper phase and in the iron phase, respectively,X_(Pt in Cu) and X_(Pt in Fe-C) are the molar fractions of platinum (Pt)in the copper phase and in the iron phase, respectively, R is the gasconstant, and T is the temperature (K).

The activity coefficient of Pt in each phase can be calculated as shownby Equations (4) and (5).

ln γ_(Pt in Fe-C)=ln γ°_(Pt in Fe)+Σε_(Pt) _(i)_(in Fe)·X_(i in Fe-C)  (4)

ln γ_(Pt in Cu)=ln γ°_(Pt in Cu)+Σε_(Pt) _(i) _(in Cu)·X_(i in Cu)  (5)

where γ°_(Pt in Fe) and γ°_(Pt in Cu) are the activity coefficients ofplatinum (Pt) in pure iron and pure copper, respectively, ε_(Pt in Fe)^(i) and ε_(Pt in Cu) ^(i) are respectively the interaction coefficientsof platinum (Pt) and element i in an iron (Fe)-platinum (Pt)-element ialloy system and a copper (Cu)-platinum (Pt)-element i alloy system, andX_(i in Fe-C) and X_(i in Cu) are respectively the molar fractions ofelement i in the iron phase and in the copper phase.

ln γ_(Pt in Fe-C)=ln γ°_(Pt in Fe)+Σ{ε_(Pt) _(i) _(in Fe)/Mi/Σ([mass %i]_(in Fe-C)/Mi)·[mass % i]_(in Fe-C)}  (6)

ln γ_(Pt in Cu)=ln γ°_(Pt in Cu)+Σ{ε_(Pt) _(i) _(in Cu)/Mi/Σ([mass %i]_(in Cu)/Mi)·[mass % i]_(in Cu)}  (6)

where [mass % i]_(in Fe-C) and [mass % i]_(in Cu) are respectively thecontents of element i in the iron phase and in the copper phase(expressed in unit of mass percent), and Mi is the atomic weight ofelement i.

In light of the above, it is clear that the distribution ratio ofplatinum (Pt) between a copper phase and an iron phase depends on theconcentration of another element i in each phase and the interactionbetween platinum (Pt) and the other element i.

In the same manner as when considering the above-described distributionratio of platinum (Pt), the concentration of the other element i in eachphase (the distribution ratio of element i between the copper phase andthe iron phase) is given by Equation (3) in which Pt is replaced byelement i. If any interaction is ignored, the tendency of distributionof element i can be predicted by γ°_(i in Fe) and γ°_(i in Cu) asenvisaged by Equations (4) and (5).

Namely, element i is concentrated in the copper phase whenγ°_(i in Fe)>>γ°_(i in Cu), element i is distributed to the same extentin each phase when γ°_(i in Fe)≈γ°_(i in Cu), and element i isconcentrated in the iron phase when γ°_(i in Fe)<<γ°_(i in Cu).

Table 1 shows the value of γ°_(i in Fe)/γ°_(i in Cu) for each element i,which was calculated based on the enthalpy of dissolution given by theMiedema model (A. K. Niessen et al, CALPHAD, Vol. 7 (1983), pp. 51-70).

TABLE 1 i γ°_(i in Fe)/γ°_(i in Cu) Cs 4239681801 Rb 814730216 K156564892 Ba 34330529 Sr 8589584 Na 613565 Ca 361941 La 9610 Nd 6055 Pb2568 Tl 2107 Ag 1728 Li 1728 Dy 1728 Bi 1515 Y 1515 Mg 642 Hg 493 In 238Au 183 Th 140 Cd 131 Sb 83 Pr 72 Sc 59 Sn 59 Cu 27 Pd 17 Zn 7.2 Ga 3.3Pu 2.7 Ge 2.7 Pt 0.88 Zr 0.59 As 0.52 Rh 0.45 Al 0.40 Mn 0.40 Hf 0.33 Ni0.27 U 0.27 Co 0.16 Be 0.13 Ti 0.11 Si 0.099 Ir 0.076 P 0.051 Tc 0.039 V0.037 Ru 0.035 Fe 0.030 Cr 0.023 Os 0.016 Ta 0.0066 Nb 0.0045 Re 0.0045Mo 0.0025 W 0.0013

From Table 1, it can be seen that Nd, Dy, and Pr have a strong tendencyto concentrate in the copper phase. In addition, it can be seen that Pthas a tendency to be distributed in both phases.

Table 2 shows the interaction coefficients in copper of elements whichconcentrate in the copper phase in Table 1 with Pt.

TABLE 2 i ε_(Pt in Cu) ^(i) ε_(Pt in Cu) ^(i)/M_(i) · 100 i ε_(Pt in Fe)^(i) ε_(Pt in Fe) ^(i)/M_(i) · 100 Pr −17.4 −12.4 Zr −12.6 −13.8 Nd−17.2 −11.9 Hf −10.9 −6.1 Dy −17.0 −10.4 U −8.0 −3.4 Th −16.8 −7.3 Ti−6.9 −14.3 La −13.0 −9.4 Nb −5.4 −5.8 Y −12.7 −14.3 Ta −5.4 −3.0 Sc−12.0 −26.7 V −1.8 −3.5 Pu −10.4 −4.3 Al −0.4 −1.5 Ba −8.3 −6.1 Mn 0.61.1 Sr −7.7 −8.8 Mo 0.9 0.9 Ca −6.9 −17.1 Cr 2.0 3.8 Cs −5.5 −4.2 W 2.11.1 Rb −4.6 −5.3 Be 2.3 25.6 Ga −4.4 −6.2 Si 3.2 11.3 K −3.6 −9.3 As 3.24.3 Mg −3.5 −14.4 Fe 4.2 7.6 Sn −3.4 −2.9 Co 5.7 9.7 In −3.1 −2.7 Re 6.33.4 Zn −1.8 −2.7 Ni 6.6 11.2 Tl −1.5 −0.7 Tc 7.4 7.5 Na −1.4 −6.0 Os 8.34.4 Li −1.4 −20.0 Ru 8.4 8.3 Cd −1.1 −1.0 Rh 8.4 8.2 Bi −1.1 −0.5 P 8.828.5 Sb −0.9 −0.8 Ir 9.9 5.1 Ge −0.8 −1.1 Pb −0.5 −0.3 Hg 0.7 0.3 Cu 0.91.5 Ag 2.8 2.6 Au 7.7 3.9 Pd 8.3 7.8

Table 2 shows the values of ε_(Pt in Cu) ^(i) or ε_(Pt in Fe) ^(i), thelatter of which is the interaction coefficient in iron of elements whichconcentrate in the iron phase with Pt and was calculated based on theenthalpy of dissolution by the Miedema model.

The values of ε_(Pt in Cu) ^(i)/Mi and ε_(Pt in Fe) ^(i)/Mi, which werecalculated by dividing the interaction coefficients by the atomic weighti, are also shown in Table 2.

The more negative the value of the interaction ε_(Pt in Cu) ^(i), thestronger the thermodynamic affinity for Pt. It can be seen from Table 2that among the elements which concentrate in the copper phase, neodymium(Nd), dysprosium (Dy), and praseodymium (Pr) have an extremely strongthermodynamic affinity for platinum (Pt). Based on Equations (6) and(7), it is necessary to evaluate ε_(Pt in Cu) ^(i)/Mi with respect to[mass % i]_(in Cu), but even in this case, it can be seen that neodymium(Nd), dysprosium (Dy), and praseodymium (Pr) have a strong effect.

As described above, Pt which is normally distributed in both phases isconcentrated in the copper phase by interaction with neodymium (Nd),dysprosium (Dy), or praseodymium (Pr) which is concentrated in thecopper phase. Examples of elements which have effects similar toneodymium (Nd), dysprosium (Dy), and praseodymium (Pr) include scandium(Sc), lithium (Li), calcium (Ca), magnesium (Mg), yttrium (Y), lanthanum(La), potassium (K), strontium (Sr), thorium (Th), gallium (Ga), barium(Ba), sodium (Na), rubidium (Rb), plutonium (Pu), cesium (Cs), tin (Sn),indium (In), and zinc (Zn).

In contrast to neodymium (Nd), dysprosium (Dy), and praseodymium (Pr),elements such as titanium (Ti), zirconium (Zr), hafnium (Hf), niobium(Nb), vanadium (V), uranium (U), and tantalum (Ta) which concentrate inan iron phase and have an extremely strong thermodynamic affinity for Pthave the property of concentrating platinum (Pt) in an iron phase.Accordingly, in a system according to the present invention whichrecovers platinum in copper-iron scrap from a molten copper phase, theseelements act as inhibiting elements.

As described above, in the present invention, using an iron (Fe)-copper(Cu)-carbon (C) system in which copper-iron scrap can be separatedrelatively easily into two liquid phases consisting of a molten copperphase and a molten iron phase, the distribution ratio of Pt, which byitself is preferentially distributed into a molten iron phase ratherthan into a molten copper phase, in the molten copper phase is increasedby making the molten copper phase contain a rare metal. Once thedistribution ratio of Pt into the molten copper phase is increased inthis manner, since technology for recovering Pt from a molten copperphase is already established in a Cu refining process, efficientrecovery of Pt contained in copper-iron scrap is realized by applyingthat technology.

There is no particular limitation on a means for making a molten copperphase contain a rare metal when separating a melt into two liquidphases. It is possible to use scrap containing a rare metal as thecopper-iron scrap, or it is possible to add a member containing a raremetal to the melt.

A typical example of scrap for use in the former means is copper-ironscrap including neodymium magnets. An example of a source of such scrapis discarded hybrid automobiles and electric automobiles. In the future,there will be an increasingly strong demand for decreases in the amountof carbon dioxide discharged from automobiles. Therefore, it is possiblethat large amounts of copper-iron scrap including neodymium magnets willbe produced.

An example of a member containing a rare metal for use in the lattermeans is processing scrap formed when processing neodymium magnets. Dueto their excellent magnetic properties, it is expected that neodymiummagnets will be used in the future in many products such as industrialequipment, transport equipment such as automobiles, and householdelectrical appliances. It is expected that such processing scrap will beproduced in large amounts in the future. From this standpoint, it ispromising as a stable supply source of members containing rare metals.

Rare metals are concentrated in a copper phase by carrying out a methodaccording to the present invention. As a result, it is possible tosimultaneously carry out separation and recovery of these rare metalswhich currently are almost completely ignored for recovery.

Using the same principles, it is possible to apply the method toseparation and recovery of other valuable metals contained in industrialequipment, transport equipment such as automobiles, household electricalappliances, and the like.

Considering the effect of an interaction with Nd on the distribution ofplatinum group elements, palladium (Pd), rhodium (Rh), ruthenium (Ru),iridium (Ir), and osmium (Os), the results are ε_(Pd in Cu)^(i)/Mi·100=−11.9, ε_(Rh in Cu) ^(i)/Mi·100=−8.7, ε_(Ru in Cu)^(i)/Mi·100=−8.0, ε_(Ir in Cu) ^(i)/Mi·100=−6.3, and ε_(Os in Cu)^(i)/Mi·100=−3.7, respectively. Thus, in the same manner as withplatinum (Pt) for which ε_(Pt in Cu) ^(i)/Mi×100=−11.9, these platinumgroup elements theoretically act to concentrate greater in a copperphase than in an iron phase.

Equation (8) is derived from Equations (3), (4), and (5) for aFe—Cu—C—Pt-i system (i:a rare metal).

log(X_(Pt in Cu)/X_(Pt in Fe-C))=log γ°_(Pt in Fe)−logγ°_(Pt in Cu)+(ε_(Pt in Fe) ^(C))(X_(C in Fe-C))+(ε_(Pt in Fe)^(i))(X_(i in Fe-C))−(ε_(Pt in Cu) ^(i))(X_(i in Cu))  (8)

As shown by the below-described examples, the logarithm of thedistribution ratio is related to the concentration of element i (i:arare metal) in the copper phase. Of the terms on the right side ofEquation (8), if terms other than those related to the concentration ofelement i (i:a rare metal) in the copper phase do not vary, thedistribution ratio depends entirely on the concentration of element i inthe copper phase. Therefore, a system according to the present inventionis not limited by the quantitative relationship between platinum andelement i (i:a rare metal).

However, from the standpoint of facilitating recovery of platinum in thecopper phase in the subsequent step of the present invention, theconcentration of Pt in the system is preferably at least 1 ppm. When itis less than 1 ppm, the concentration of platinum in the copper phase islow even if platinum is concentrated by the method according to thepresent invention, so even if platinum is recovered using a Cu refiningprocess, the recovery cost per unit mass becomes too high and the methodbecomes inefficient.

Equation (8) can be applied to a case in which a small amount of anelement is dissolved in a large amount of solvent. Considering thetheoretical effect of the present invention, the concentration ofplatinum in the system is preferably at most 2 mass percent.

From the same point of view, the concentration of element i (i:a raremetal) in the system is limited. An upper limit on the concentration ofelement i (i:a rare metal) in the copper phase is set by Equation (8).Although this upper limit is not definite, from the fact that aprominent distribution promoting ability is ascertained even when Nd is7.3% in the below-described examples, it is estimated that the upperlimit is generally on the order of 10 mass percent.

In present invention, an extremely small amount of element i (i:a raremetal) theoretically provides an effect. However, from the standpoint offacilitating recovery of platinum in the copper phase in the subsequentstep in the present invention, it is particularly preferable for thetotal concentration of element i (i:a rare metal) in the copper phase tobe at least 1 mass percent so as to achieve a distribution ratio of atleast 1.7.

Concerning the concentration of element i, in a preferred embodiment ofa method according to the present invention, a metal (referred to belowas a distribution promoting metal) having the ability to increase thedistribution of platinum in a molten copper phase (referred to below asa distribution promoting ability) in the same manner as a rare metalwhile not being a rare metal is contained in melt to increase thedistribution of Pt. As can be understood from Tables 1 and 2, examplesof such elements are Sc, Li, Ca, Mg, Y, La, K, Sr, Th, Ga, Ba, Na, Rb,Pu, Cs, Sn, In, and Zn.

On the premise that the molten copper phase is a dilute solution asdescribed above, the distribution promoting ability of thesedistribution promoting metals can be said to be independent of eachother from the following Equation (9) which is derived from aboveEquation (3), (6), and (7).

$\begin{matrix}{{\ln \left( {X_{{Pt}\mspace{14mu} {in}\mspace{14mu} {Cu}}/X_{{{Pt}\mspace{14mu} {in}\mspace{14mu} {Fe}} - C}} \right)} = {{\ln \; \gamma_{{Pt}\mspace{14mu} {in}\mspace{14mu} {Fe}}^{0}} - {\ln \; \gamma_{{Pt}\mspace{14mu} {in}\mspace{14mu} {Cu}}^{0}} + {\sum\; \left\{ {{ɛ_{{Pt}\mspace{14mu} {in}\mspace{14mu} {Fe}}^{i}/{Mi}}/{\sum\; {\left( {\left\lbrack {{mass}\mspace{14mu} \% \mspace{14mu} i} \right\rbrack_{{{in}\mspace{14mu} {Fe}} - C}/{Mi}} \right) \cdot \left\lbrack {{mass}\mspace{14mu} \% \mspace{14mu} i} \right\rbrack_{{{in}\mspace{14mu} {Fe}} - C}}}} \right\}} - {\sum\; \left\{ {{ɛ_{{Pt}\mspace{14mu} {in}\mspace{14mu} {Cu}}^{i}/{Mi}}/{\sum\; {\left( {\left\lbrack {{mass}\mspace{14mu} \% \mspace{14mu} i} \right\rbrack_{{in}\mspace{14mu} {Cu}}/{Mi}} \right) \cdot \left\lbrack {{mass}\mspace{14mu} \% \mspace{14mu} i} \right\rbrack_{{in}\mspace{14mu} {Cu}}}}} \right\}}}} & (9)\end{matrix}$

By calculating the following Equation (10) for these distributionpromoting metals, the distribution promoting ability of thesedistribution promoting metals can be evaluated relative to Nd.

(ε_(Pt in Cu) ^(i)/M_(i))/(ε_(Pt in Cu) ^(Nd)/M_(Nd))  (10)

The results of calculation of Equation (10) are as follows.

-   -   Sc: 2.2, Li: 1.7, Ca: 1.4, Mg: 1.2, Y: 1.2, La: 0.79, K: 0.78,        Sr: 0.74, Th: 0.61, Ga: 0.52, Ba: 0.54, Na: 0.50, Rb: 0.45, Pu:        0.36, Cs: 0.35, Sn: 0.24, In: 0.23, and Zn: 0.23.

For rare metals, Nd: 1, Pr: 1, and Dy: 0.87.

From the above, it can be seen that Sc, Li, Ca, Mg, and Y have a higherdistribution promoting ability than rare metals. Accordingly, it istheoretically possible to recover platinum from a molten copper phasewith a higher recovery rate by containing these elements than when usinga rare metal. However, scrap containing these elements as a metal isscarce, so in actual practice, it is necessary to charge these metalsinto a melt of copper-iron scrap. This of course increases the recoverycost per unit mass of platinum. Accordingly, from the standpoint ofstably and inexpensively obtaining a raw material for distributionpromoting metals, it is preferable to use rare metals as distributionpromoting metals as in the present invention.

On the other hand, by suppressing the content of metals (referred tobelow as distribution inhibiting metals) having the ability to inhibitthe above-described distribution promoting ability (referred to below asa distribution inhibiting ability) by increasing the distribution ofplatinum in the molten iron phase, which is the opposite of the actionof rare metals, it is possible to suppress a decrease in thedistribution of Pt in the molten copper phase. As can be seen fromTables 1 and 2, examples of such distribution inhibiting metals are Ti,Zr, HF, Nb, V, U, and Ta. In the same manner as the above-describeddistribution promoting metals, the distribution inhibiting ability ofthe distribution inhibiting metals can be evaluated relative to Nd basedon the following Equation (11).

(ε_(Pt in Fe) ^(i)/M_(i))/(ε_(Pt in Cu) ^(Nd)/M_(Nd))  (11)

The results are Ti: 1.2, Zr: 1.2, Hf: 0.51, Nb: 0.49, V: 0.29, U: 0.29,and Ta: 0.25

Based on the relative values of the ability of distribution promotingmetals and distribution inhibiting metals which are quantified in thismanner, the amount of elements i which are contained in the moltencopper phase or the molten iron phase after separation into two liquidphases preferably satisfie the following Equation (12).

2.2Sc+1.7Li+1.4Ca+1.2Mg+1.2Y+Nd+Pr+0.87Dy+0.79La+0.78K+0.74Sr+0.61Th+0.52Ga+0.51Ba+0.50Na+0.45Rb+0.36Pu+0.35Cs+0.24Sn+0.23In+0.23Zn−(1.2Ti+1.2Zr+0.51Hf+0.49Nb+0.29V+0.29U+0.25Ta)>1mass %  (12)

where the symbol for each element indicates the mass concentration(units of mass percent) of the corresponding element in the moltencopper phase with respect to the mass of the molten copper phase fordistribution promoting metals and rare metals, and it indicates the massconcentration (units of mass percent) of the corresponding element inthe molten iron phase with respect to the mass of the molten iron phasefor distribution inhibiting metals.

A suitable temperature for the present invention is 1445-2920 K at whichit is possible to maintain two-phase separation in a Fe—Cu—C system.However, melting at a temperature higher than 1973 K requires a largeamount of energy for heating. Therefore, from the standpoint of energycosts, the melting temperature is preferably at most 1973 K. As thetemperature increases, the movement of atoms becomes more active and theeffect of the interaction between atoms decreases. Namely, thedifference in the thermodynamic affinity between elements (the functionof promoting distribution) becomes stronger as the temperaturedecreases. For this reason, it is preferable to carry out the method ata low temperature.

The distribution ratio given by Equation (8) does not depend on the massratio of the molten iron phase and the molten copper phase, sotheoretically, as far as the effect of the present invention isconcerned, there is no limitation on the mass ratio of the molten ironphase and the molten copper phase. However, when it is desired toachieve at least a predetermined value a with respect to the ratio ofthe mass of platinum contained in the molten copper phase W_(Pt in Cu)to the total mass of platinum contained in the copper-iron scrap W_(Pt),i.e., the recovery rate, it is possible to specify the range to besatisfied by the proportion R (=W_(Cu)/W_(Total)) of the mass W_(Cu) ofthe molten copper phase with respect to the total mass W_(Total) of themolten copper phase and the molten iron phase by the following Equation(13) based on the lower limit a of the recovery rate and thedistribution ratio k (the platinum concentration in the molten copperphase/the platinum concentration in the molten iron phase).

R≧a/{(1−a)k+a}  (13)

For example, according to the below-described examples, when [massNd]_(in Cu) is 3.59 mass %, the distribution ratio k is 2.62.Accordingly, in order to achieve a recovery rate of at least 70% withthis distribution ratio, since the lower limit value a is 0.7, R shouldbe at least 0.47 or R≧0.47 (=0.7/1.486). In order to achieve a recoveryrate of at least 90%, R≧0.77 (=0.9/1.162). Thus, when attempting toincrease the recovery rate, it is preferable to set the mass proportionR of the molten copper phase to a high value, such as by additionallycharging copper into copper-iron scrap. The copper which is additionallycharged functions as a solvent, so it can of course be repeatedly used.

Above-described Equation (13) can be derived from the followingrelationship.

When the mass of platinum contained in the molten iron phase isexpressed as W_(Pt in Fe-C) and the mass of the molten iron phase isexpressed as W_(Fe-C), the distribution ratio k, the total mass ofplatinum contained in the molten iron scrap W_(Pt), and the total massof the molten copper phase and the molten iron phase W_(Total) are givenby the following Equations (14)-(16).

k=(W_(Pt in Cu)/W_(Cu))/(W_(Pt in Fe-C)/W_(Fe-C))  (14)

W_(Pt)═W_(Pt in Cu)+W_(Pt in Fe-C)  (15)

W_(Total)═W_(Cu)+W_(Fe-C)  (16)

The following Equation (17) is derived by canceling W_(Pt in Fe-C) andW_(Fe-C) from the above three equations.

W_(Pt in Cu) =k·W_(Cu)·W_(Pt)/{W_(Total)+(k−1)·W_(Cu)}  (17)

The recovery rate is defined as W_(Pt in Cu)/W_(Pt) and is greater thanor equal to a. Therefore, by substituting W_(Pt in Cu)/W_(Pt)≧a intoabove Equation (17), above Equation (13) is obtained.

The higher the carbon concentration in the molten iron phase, thegreater is the ability to separate the molten iron phase from the moltencopper phase, namely, the lower is the copper concentration incorporatedin the molten iron phase. Therefore, rather than using a cupola whichproduces a weakly reducing atmosphere, it is preferable to use acarbonaceous material-packed bed which produces a strongly reducingatmosphere and causes a larger amount of carbon to dissolve as anapparatus for increasing the effect of the present invention.

EXAMPLES

The following examples are intended to specifically illustrate thepresent invention.

Example 1

5 grams of C-saturated Fe, 5 grams of Cu, and 0.05 grams of Pt wereplaced into a graphite crucible. In each experiment, under conditions inwhich from 0.7 to 1 gram of Au, Ag, In, Dy, or W was or was not added,the mixture was melted at 1823 K using an electric furnace in anatmosphere containing 100 ml/min of Ar (converted to standardconditions) and held for 2 hours. The sample was then removed from thefurnace and cooled by blowing Ar gas.

Table 3 shows the concentration of added element i in the copper phase[mass % i]_(in Cu) and the concentration of added element i in the ironphase [mass % i]_(in Fe-C) in the sample after cooling, the distributionratio of i in the copper phase/iron phase [mass % i]_(in Cu)/[mass %i]_(in Fe-C), and the distribution ratio of Pt [mass % Pt]_(in Cu)/[mass% Pt]_(in Fe-C). The results of experiments in which no element wasadded are also shown.

TABLE 3 Element i — — — Au Ag In Dy W [mass % i]_(in Cu) — — — 0.91 1.020.98 0.53 0.001 [mass % i]_(in Fe—C) — — — 0.01 0.003 0.001 0.18 0.92[mass % i]_(in Cu)/[mass % i]_(in Fe—C) — — — 91 340 980 2.9 0.0011[mass % Pt]_(in Cu)/[mass % Pt]_(in Fe—C) 1.21 1.22 1.28 1.30 1.19 1.251.44 1.24 Symbol in FIG. 1 ⊚ Δ ▴ □ ▪ ∇

From the results shown in Table 3, it can be seen that Au, Ag, In, andDy were concentrated in the Cu phase and W was concentrated in the Fephase.

FIG. 1 shows the relationship between the logarithm of the distributionratio of Pt and the concentration of added element i in the copperphase. A change in the distribution ratio of Pt due to concentrated Au,Ag, and In in the copper phase was not observed, but it can be seen thatthe distribution ratio of Pt was increased by containing Dy. Inaddition, it can be seen from FIG. 1 that W distributed into the ironphase did not affect the distribution of Pt.

Example 2

5 grams of carbon-saturated iron, 5 grams of a combination of acopper-neodymium alloy and copper in predetermined different proportionsin order to vary the neodymium concentration in the copper, and 0.05grams of platinum were placed into a graphite crucible. Using anelectric furnace, the mixture was melted at 1823 K in an atmosphere of100 ml/min of argon gas (converted to standard conditions) and held for2 hours. The sample was then removed from the furnace and cooled byblowing argon gas.

Table 4 shows the neodymium concentration in the copper phase [mass %Nd]_(in Cu) and the neodymium concentration in the iron phase [mass %Nd]_(in Fe-C) in the sample after cooling, and the distribution ratio ofneodymium [mass % Nd]_(in Cu)/[mass % Nd]_(in Fe-C). FIG. 2 shows theresults of plotting this data with the neodymium concentration in thecopper phase on the abscissa and the common logarithm of thedistribution ratio of neodymium on the ordinate.

TABLE 4 [mass % Nd]_(in Cu) 0.4 0.57 3.59 7.3 [mass % Nd]_(in Fe—C) 0.060.09 0.86 1.38 [mass % Nd]_(in Cu)/[mass % Nd]_(in Fe—C) 6.7 6.3 4.2 5.3[mass % Pt]_(in Cu)/[mass % Pt]_(in Fe—C) 1.85 1.53 2.62 8.70 Symbol inFIG. 2 

From these figures and tables, it can be seen that neodymium isconcentrated in the copper phase due to the presence of neodymium in thecopper phase, and that the larger the amount of neodymium in the copperphase, the more concentration into the copper phase progresses.

From the above-described results, it can be seen that the method of thepresent invention effectively utilizes rare metals in copper-iron scrap,and that the method results in efficiently recovery of Pt byconcentrating Pt into a copper phase with a high distribution ratio.

1. A method of recovering a platinum group element in copper-iron scrapcharacterized by melting copper-iron scrap containing a platinum groupelement to form a melt, forming the melt into two liquid phases whichare a molten copper phase containing at least one rare metal selectedfrom the group consisting of Nd, Pr, and Dy and a molten iron phasehaving a carbon concentration of at least 1 mass %, wherein the carboncontained in the molten iron phase is derived from a carbon sourcecontained in the melt, separating the two liquid phases and recoveringthe molten copper phase, and separating and recovering a platinum groupelement dissolved in the molten copper phase from the molten copperphase.
 2. A method as set forth in claim 1 wherein the molten copperphase containing the rare metal is formed by using scrap containing therare metal as the copper-iron scrap.
 3. A method as set forth in claim 1wherein the molten copper phase containing the rare metal is formed byadding a member containing the rare metal to the melt.
 4. A method asset forth in claim 1 wherein the total concentration of the rare metalcontained in the molten copper phase is at least 1 mass %.
 5. A methodas set forth in claim 1, wherein the melt contains at least onedistribution promoting element selected from the group consisting of Sc,Li, Ca, Mg, Y, La, K, Sr, Th, Ga, Ba, Na, and Rb, and/or at least onedistribution inhibiting element selected from the group consisting ofTi, Zr, Hf, Nb, V, U, and Ta, and the two liquid phases which are themolten copper phase and the molten iron phase and into which the melt isseparated satisfy the following Equation (i):2.2Sc+1.7Li+1.4Ca+1.2Mg+1.2Y+Nd+Pr+0.87Dy+0.79La+0.78K+0.74Sr+0.61Th+0.52Ga+0.51Ga+0.50Na+0.45Rb+0.36Pu+0.35Cs+0.24Sn+0.231n+0.23Zn−(1.2Ti+1.2Zr+0.51Hf+0.49Nb+0.29V+0.29U+0.25Ta)>1.0mass %  (i) wherein, the symbol for each element in Equation (i)indicates the mass concentration (units of mass percent) of thecorresponding element in the molten copper phase with respect to themass of the molten copper phase in the case of the distributionpromoting metals and the rare metals and indicates the massconcentration (units of mass percent) of the corresponding element inthe molten iron phase in the case of the distribution inhibiting metalswith respect to the mass of the molten iron phase.